(function (doc, win) {
var docEl = doc.documentElement,
	resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
	recalc = function () {
	  var clientWidth = docEl.clientWidth;
	  if (!clientWidth) return;
	  docEl.style.fontSize = 100 * (clientWidth / 750) + 'px'; 
	};

if (!doc.addEventListener) return;
win.addEventListener(resizeEvt, recalc, false);
doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window); 
 